The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a through electrode which forms a three-dimensional semiconductor device, and to a method of manufacturing such a semiconductor device.
Three-dimensional semiconductor devices having a plurality of stacked semiconductor devices have been proposed in recent years. In these three-dimensional semiconductor devices, the respective semiconductor devices are electrically connected to each other by through electrodes, which extend through semiconductor substrates.
FIGS. 1 and 2 show a conventional three-dimensional semiconductor device. The three-dimensional semiconductor device shown in FIG. 1 has three semiconductor devices 3, 4, and 5 and a support substrate 1 on which the semiconductor devices 3, 4, and 5 are mounted. Each semiconductor device has a through electrode 7 extending through a semiconductor substrate. The semiconductor devices are connected to each other by bumps 6, which are connected to the through electrodes 7, and also connected to a wiring pattern 2 on the support substrate 1. FIG. 2 is a cross-sectional view of one through electrode 7. The illustrated through electrode 7 is produced after completion of a wiring process in a semiconductor fabrication process.
An opening is formed in an insulation film 17 in a state in which interconnections 16 are formed in the semiconductor device. A trench is formed in the semiconductor substrate 11. A through electrode insulation film 7b is deposited on an inner wall of the trench. Further, the trench is filled with a through electrode conductive film 7a. Then, an upper surface of the through electrode conductive film 7a is flattened by CMP or the like so as to have the same height as a surface of the semiconductor. A rear face of the semiconductor substrate 11 is ground so that the semiconductor substrate 11 has a predetermined thickness. A rear insulation film 18 is deposited on the rear face of the semiconductor substrate 11. Then, an opening is formed in the rear insulation film 18, and a bump 19 is formed in the opening. A bump 19 may be formed on the front face of the semiconductor substrate as needed. If no bump is formed on the semiconductor substrate, a protective insulation film is formed on the semiconductor substrate.
These through electrodes are used as power source lines and signal lines. Accordingly, It is desirable that the through electrodes have a low wiring resistance and a small stray capacitance. Through electrodes having a high wiring resistance cause reduction of a voltage and delay of signals to thereby lower an operating speed. Finally, the semiconductor may not work. Further, if through electrodes have a large capacity, a signal waveform is disturbed by delay of signals and noise between signals, so that high-speed data transfer cannot be performed. Accordingly, in order to reduce a resistance of a through electrode, it is necessary to increase a diameter of a trench formed in a semiconductor substrate and fill the trench with a conductive film. Further, in order to reduce a capacity of a through electrode, it is necessary to thicken an insulation film between a semiconductor substrate and a conductive film and to use an insulation film having a small dielectric constant. However, only limited types of insulation films can be used in a semiconductor fabrication process. As a result, it is necessary to increase a film thickness of an insulation film.
Accordingly, in order to produce a through electrode, a trench having a diameter of several tens of micrometers should be formed in a semiconductor substrate, and a through electrode insulation film 7b should be deposited as thick as several micrometers to several tens of micrometers. In the prior art, when a conductive film or an insulation film having a film thickness in the above range, deposition should be performed for a long period of time. Thus, a heavy load is imposed on a manufacturing process. Further, in a case of deposition of a conductive film having a thickness of several tens of micrometers, the deposited grain becomes non-uniform as the film thickness becomes larger. The non-uniform grain causes variation of properties of the conductive film so as to increase a resistivity of the conductive film. Thus, it has been desired to develop a structure of a through electrode having a low resistance and a small capacity, and to establish a method of manufacturing such a through electrode.
Japanese laid-open patent publications Nos. 2003-017558 and 2002-289623 relate to through electrodes. Japanese laid-open patent publication No. 2003-017558 discloses forming a trench having a diameter of several tens of micrometers in a semiconductor substrate, then filling the trench with an application insulation film, etching the semiconductor substrate to form a trench in the semiconductor substrate, and depositing a conductive film in the trench to produce a through electrode with the conductive film having no cavities. Japanese laid-open patent publication No. 2002-289623 discloses a second insulation area provided outside of a through electrode to prevent short-circuits between the through electrode and a semiconductor substrate.
Japanese laid-open patent publications Nos. 2005-094044, 2004-228308, 08-078699, and 2004-273483 relate to methods of forming a via hole, a through hole, and a contact hole. Japanese laid-open patent publications Nos. 2005-094044 and 2004-228308 disclose that insulation films having different etching rates are deposited on an upper side of a gate electrode and on a side surface of the gate electrode to form self-aligning contact. Japanese laid-open patent publication No. 08-078699 discloses forming a diffusion layer while using a gate electrode as a mask. Japanese laid-open patent publication No. 2004-273483 discloses an etching method for forming a hole in an interlayer dielectric. However, these publications fail to teach or disclose a structure of a through electrode having a small capacity with respect to a semiconductor substrate and a low resistance, and a method of manufacturing such a through electrode.
As described above, a conventional through electrode used in a three-dimensional semiconductor device has the following problems: The resistance of the through electrode is so large that high-speed data transfer cannot be performed. A deposition time of an embedded conductive film becomes long because the embedded conductive film of the through electrode should have a large film thickness.